Method of producing viscose rayon



United States Patent Martini) or PRODUCING vrscosu RAYON Wayne A. Sisson, Media, Pa., assignor to American Viscose Corporation, Philadelphia, Pa., a corporation of Delaware Claims. (Cl. 106-165) This invention relates to the production of shaped bodies of regenerated cellulose from viscose and more particularly to filaments and fibers of regenerated cellulose from viscose.

In the conventional methods of producing shaped bodies of regenerated cellulose from viscose, a suitable cellulosic material such as purified cotton linters, Wood pulp, mixtures thereof, and the like is first converted to an alkali cellulose by treatment with a caustic soda solution and after shredding the treated cellulose material, it is allowed to age. The aged alkali cellulose is then converted to a xanthate by treatment with carbon disulfide. The cellulose xanthate is subsequently dissolved in a caustic soda solution in an amount calculated to provide a viscose of the desired cellulose and alkali content. After filtration, the viscose solution is allowed to ripen and is subsequently extruded through a shaped orifice into a suitable coagulating and regenerating bath.

In the production of shaped bodies such as filaments, the viscose solution is extruded through a spinneret into a coagulating and regenerating bath consisting of an aqueous acid solution containing zinc sulfate. The filament may subsequently be passed through a hot aqueous bath where it is stretched to improve its properties such as tensile strength. The filament may then be passed through a dilute aqueous solution of sulfuric acid and sodium sulfate to complete the regeneration of the cellulose, in case it is not completely regenerated upon leaving the stretching stage. The filament is subsequently subjected to washing, purification, bleaching, possibly other treating operations and drying, being collected either before or after tliese treatments.

The filaments as formed by the convention methods, consist of a skin or outer shell portion and a core portion with a sharp line of demarkation between the two. The cross-section of the filaments exhibits a very irregular or crenulated exterior surface when even small amounts of zinc salts or certain other polyvalentmetal salts are present in the spinning bath. The skin and core portions of the filament represent difierences in structure and these difierent portions possess different swelling and staining characteristics, the latter permitting a ready identification of skin and core. The sharply irregular and crenulated surface structure has a relatively low abrasion resistance and readily picks up foreign particles such as dirt. Although the core portion possesses a relatively high tensile strength, it has a low abrasion resistance and a low flex-life, is subject to fibrillation and is relatively stiff.

It has now been discovered that the presence of small amounts of water-soluble alkylene oxide adducts of urea and biuret in viscose, in the spinning bath, or in both the viscose and the bath results in the productionof shaped bodies of regenerated cellulose such as filaments, films, sheets and the like composed of all skin and having improved properties and characteristics providing that the amount of the adduct is maintained with certain product.

. Patented se t. 29, 1959 ice , 2 limits and the composition of the spinning bath is maintained within certain composition limits which will be defined hereinafter. The most readily distinguishable characteristics as-compa red to conventional filaments include a smooth, nonecrenulated surface and the filaments consist entirely of skin.

This invention contemplates the use of alkylene oxide adducts of urea and biuret having up to or more alkylene oxide groups per molecule, preferably from about 4 to about 50 alkylene oxide units per molecule of urea or biuret. It is obvious that for all practical purposes considering cost, ease of preparation, commercial availability and solubility in water, in alkali solutions and in acid solutions, the ethylene oxide adducts are preferred. Theoretically, an alkylene oxide adduct such as ethylene oxideadduct of urea containing 4 ethylene oxide units per molecule of urea would consist of a compound in which each of the amino hydrogen atoms has been replaced with an ethanol radical. It is not necessary, however, that all of the amino hydrogens be replaced nor is it necessary that the ethylene oxide chains replac ing the different hydrogen atoms be the same in each instance.

The production of all skin products requires that certain minimum amounts of the alkylene oxide adduct bein solution in the viscose or in the spinning bath. Therefore, the alkylene oxide adduct must have sufiicient solubility to permit the minimum amount of the adduct to be dissolved in the viscose or the spinning bath or both. The adduct may be conveniently added to the viscose in the form of a solution in alkali or water and to the spinning bath in a solution of water or of the spinning bath.

Where the alkylene oxide adduct of urea is to be added, to the viscose, the amount of the adduct which is incorporated in viscose must be at least about 0.25% by Weight of the cellulose in the viscose and may vary up to about 4%, preferably, the amount varies from 0.5% to 2.5%. Lesser amounts do not result in the production of products consisting entirely of skin and greater amounts affect adversely the physical properties of the products. Amounts within the preferred range are most eifective in enhancing the characteristics and properties of the products. The adduct of urea may be added at any desired stage in the production of the viscose suchv as in the preparation of the refined wood pulp for the manufacture of viscose, before or during the shredding of the alkali cellulose, to the xanthated cellulose while. it is being dissolved in the caustic solution or to the viscose solution before or after filtration. The adduct is preferably added after the cellulose xanthate has been dissolved in the caustic solution and prior to filtration.

The viscose may contain from about 6% to about 8% cellulose, the particular source of the cellulose being se-v lected for the ultimate use of the regenerated cellulose The caustic soda content may be from about 4% to about 8% and the carbon disulfide content may be from about 30% to about 50% based upon the weight of the cellulose. The modified viscose, that is, a viscose' containing the small amount of adduct, may have a salt test above about 7 and preferably above about 9' at the time of spinning or extrusion.

In order to obtain the improvements enumerated here-i inbefore, it is essential that the composition of the spin-: ning bath be maintained within a Well defined.range;l The presence of the alkylene oxide adducts of urea, in the viscose or in the spinning bath combined with these limited spinning baths results in the production of yarns of improved properties such as high tenacity,- high abra' sion resistance, high fatigue resistance and consisting" f filaments composed entirely of skin.

Genetically and in terms of the industrial art, the spinning bath is a low acid-high zinc spinning bath. The bath should contain from about 10% to about 25% sodium sulfate and from about 3% to about 15% zinc sulfate, preferably from 15% to 22% sodium sulfate and from 4% to 9% zinc sulfate. Other metal sulfates such as iron, manganese, nickel and the like may be present and may replace some of the zinc sulfate. The temperature of the spinning bath may vary from about 25 C. to about 80 C., preferably between about 45 C. to about 70 C. In the production of the all skin type filaments, the temperature of the spinning bath is not critical, however, as is well known in the conventional practice in the art, certain of the physical properties such as tensile strength vary directly with the temperature of the spinning bath. Thus, in the production of filaments for tire cord purposes in accordance with the method of this invention, the spinning bath is preferably maintained at a temperature between about 55 C. and 65 C. so as to obtain the desired high tensile strength.

The acid content of the spinning bath is balanced against the composition of the viscose. The lower limit of the acid concentration, as is well known in the art, is just above the slubbing point, that is, the concentration at which small slubs of uncoagulated viscose appear in the strand as it leaves the spinning bath. For commercial operations, the acid concentration of the spinning bath is generally maintained about 0.4% to 0.5% above the slubbing point. For any specific viscose composition, the acid concentration of the spinning bath must be maintained above the slubbing point and below the point at which the neutralization of the caustic of the viscose is sufiiciently rapid to form a filament having a skin and core. There is a maximum acid concentration for any specific viscose composition beyond which the neutralization is sufiiciently rapid to produce filaments having a skin and core. For example, in general, the acid concentration of the spinning baths which are satisfactory for the production of the all skin products from a 7% cellulose, 6% caustic-viscose and containing the adducts of urea lies between about and about 7.8%. The acid concentration may be increased as the amount of adduct is increased and also as the salt test of the viscose is increased. There is an upper limit, however, for the acid concentration based upon the amount of additive and the concentration of caustic in the viscose. All skin products cannot be obtained if the acid concentration is increased above the maximum value although the amount of the adduct of urea is increased beyond about 4% while other conditions are maintained constant. Increasing the caustic soda content of the viscose beyond about 8% is uneconomical for commercial production methods. For example, a viscose containing about 7% cellulose, about 6% caustic soda, about 41% carbon disulfide, 2% of an ethylene oxide adduct of urea containing about 20 ethylene oxide units per molecule and having a salt test of about when extruded into spinning baths containing 16 to 20% sodium sulfate, 4 to 8% zinc sulfate and sulfuric acid not more than about 7.8%, results in the production of all skin filaments. Lesser amounts of sulfuric acid may be employed. Greater amount of sulfuric acid result in the production of products having skin and core. A lowering of the amount of adduct of urea, the lowering of the caustic soda content or the lowering of the salt test of the viscose reduces the maximum permissible acid concentration for the production of all skin filaments. In any event, it has been determined that the maximum concentration of acid which is permissible for the production of all skin products is about 8%.

The presence of the adducts of urea in the viscose retards the coagulation and, therefore, the amount of adduct employed must be reduced at high spinning speeds. Thus, for optimum physical characteristics of must, of course, be immersed or maintained in the spin-' ning bath for a period sufficient to efiect relatively complete coagulation of the viscose, that is, the coagulation must be sutficient so that the filaments Will not adhereto each other as they are brought together and withdrawn from the bath.

In the production of filaments for such purposes as the fabrication of tire cord, the filaments are preferably stretched after removal from the initial coagulating and regenerating bath. From the initial spinning bath, the filaments may be passed through a hot aqueous bath which may consist of hot water or a dilute acid solution and may be stretched from about 70% to about 120%, preferably between and Yarns for other textile purposes may be stretched as low as 20%. The precise amount of stretching will be dependent upon the desired tenacity and other properties and the specific type of product being produced. it is to be understood that the invention is not restricted to the production of filaments and yarns but it is also applicable to other shaped bodies such as sheets, films, tubes and the like. The filaments may then be passed through a final regenerating bath which may contain from about 1% to about 5% sulfuric acid and from about 1% to about 5% sodium sulfate with or without small amounts of zinc sulfate if regeneration has not previously been com- 'pleted.

The treatment following the final regenerating bath, or the stretching operation where regeneration has been completed, may consist of a Washing step, a desulfurizing step, the application of a finishing or plasticizing material and drying before or after collecting, or may include other desired and conventional steps such as bleaching and the like. The treatment after regeneration will be dictated by the specific type of shaped body and the proposed use thereof.

Regenerated cellulose filaments prepared from viscose containing the small amounts of the Water-soluble alkylene oxide adducts of urea and spun in the spinning baths of limited acid content have a smooth or non-crenulated surface and consist substantially entirely of skin. Because of the uniformity of structure throughout the filament, the swelling and staining characteristics are uniform throughout the cross-section of the filament. Filaments produced pursuant to this invention and consisting entirely of skin have a high toughness and a greater flexing life than filaments as produced according to prior methods which may be attributed by the uniformity in skin structure throughout the filament. Although the twisting of conventional filaments, as in the production of tire cord, results in an appreciable loss of tensile strength, there is appreciably less loss in tensile strength in the production of twisted cords from the filaments consisting entirely of skin. Filaments prepared from viscose containing the adducts of urea have a high tensile strength as compared to normal regenerated cellulose filaments, have superior abrasion and fatigue resistance characteristics and have a high flex-life. Such filaments are highly satisfactory for the production of cords for the reinforcement of rubber products such as pneumatic tire casings, but the filaments are not restricted to such uses and may be used for other textile applications.

Like improvements in the characteristics and properties of the products are also obtained by incorporating the alkylene oxide adducts of urea or biuret in the spinning bath in place of adding the adduct to the viscose. It is essential that the composition of the spinning bath,

particularly the acid concentration be maintained within the limits set forth hereinbefore. In order to produce products consisting of all skin, the amount of the alkylene oxide adduct of urea dissolved in the spinning bath must be at least about 0.05% by weight and is preferably maintained at about 0.1%. The upper limit does not appear to be critical as in the incorporation of the adducts in the viscose. The upper limit is dependent upon the solubility of the particular adduct and by economic con siderations since amounts exceeding about 0.2% are not more effective in improving the properties of the prod ucts.

' It is obvious that the adducts may be added to both the viscose and the spinning bath, if desired. In such instance, it is also essential to maintain the amounts of the adduct in the viscose and in the spinning bath, and the composition of the spinning bath within the stated limits. The all skin products of improved properties are obtained only when the spinning operation in the presence of the alkylene adducts of urea or bi uret is carried out within the spinning bath composition as set forth hereinbefore. a

The invention may be illustrated by reference to the preparation of regenerated cellulose filaments froma viscose containing about 7% cellulose, about 6% caustic soda, and having a total carbon disulfide content of about 41%. The viscose solutions were prepared by xanthating alkali cellulose by the introduction of 36% carbon disulfide based on the weight of the cellulose and churning for about 2% hours. The cellulose xanthate was then dissolved in caustic soda solution. An additional 5% carbon disulfide Was then added to the mixer and the mass mixed for about one hour. The viscose was then allowed to ripen for about 30 hours at 18 C. In those instances where the modifier was incorporated in the viscose, the desired amount of an ethylene oxide adduct of urea was added to the solution and mixed for about V2 hour before allowing the viscose to ripen.

Example 1 Approximately 1% (based on the weight of the cellulose) of an ethylene oxide adduct of urea containing about 20 units of ethylene oxide per molecule of urea was added to and incorporated in the viscose as described above. The viscose employed in the spinning of filaments had a salt test of 10.4. The viscose was extruded through a spinneret to form a 1650 denier, 720 filament cord at a rate of about 22 meters per minute. The coagulating and regenerating bath was maintained at a temperature of about 60 C. and contained 7.2% sulfuric acid, 8% zinc sulfate and 17% sodium sulfate. The cord was stretched about 90%, washed free of acids and salts by treatment with water at about 95 C. on thread advancing reels, dried and collected on cones.

The individual filaments have a smooth, non-crenulated exterior surface and consist entirely of skin, no core being detectable at high magnification (e.g. 1500 The filaments of a control yarn spun with the same vistime but without the addition of the modified agent and spun under the same conditions, exhibit a very irregular and serrated surface and are composed of about 75% skin and the balance core with a sharp line of demarkation'between the skin and core. Other physical properties are set forth in the table which follows the examples.

Example 2 To a viscose solution as described above, there was added 1% of an ethylene oxide adduct of urea containing about 40 ethylene oxide units per molecule of urea. The viscose had a salt test of 10.4 and was spun into a 1650 denier, 720 filament cord by extrusion into abath containing 7.2% sulfuric acid, 8% zinc sulfate and 17% sodium sulfate. The bath was maintained at a tempera ture of 60 C. The extrusion rate was about 22 meters per minute. The cord was stretched about washed free of acids and salts by treatment with water at about C. on thread-advancing reels, dried and collected on cones.

The individual filaments were readily distinguishable Example 3 A viscose solution as described above (no adduct added) having a salt test of 9.7 was spun into a 210 denier, filament yarn by extrusion into a spinning bath containing 7. 6% sulfuric acid, 7.9% zinc sulfate, 19% sodium sulfate and 0.1% of an ethylene oxide adduct of urea containing about 20 ethylene oxide units per molecule of urea. 'Ihe bath was maintained at 60 C. and the extrusion rate was about 22 meters per minute. The filaments were passed through a hot water bath maintained at about 95 C. and stretched about 82%. The yarn was collected in a spinning box, washed free ofacid and salts and dried.

The filaments have a smooth, non-crenulated surface and consist entirely of skin while control filaments have a very irregular and serrated surface and consist of about 75 skin and the balance core with a sharp line of demarkation between the skin and core. Other physical characteristics are set forth in the table which follows the examples.

Example 4 .To a viscose as described above, there was added'2% of an ethylene oxide adduct of urea containing 4 ethylene oxide units per molecule of urea. The viscose had a salt test of 9.0 and was spun into a 210 denier, 120 filament yarn by extrusion into a spinning bath containing 7.6% sulfuric acid, 8% zinc sulfate, 19% sodium sulfate, and 0.1% of an ethylene oxide adduct of urea containing 20 ethylene oxide units per molecule of urea.

The bath was maintained at 60 C. and the extrusionrate was about 22 meters per minute. The filaments were subsequently passed through a hot water bath at 19 C. and stretched about 82%. The yarn was collected in spinning box, washed free of acids and salts and dried.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 75 skin and the balance core with a sharp line of demarkation between the skin and the core. Other physical propertiesare set forth in the table which follows the examples.

Example 5 To a viscose as described above, there was added 1% of an ethylene oxide adduct of urea containing 20 ethylene oxide units per molecule of urea. The viscose had a salt test of 11 and was spun into a 210 denier, 120 filament yarn by extrusion into a spinning bath containing 7.6% sulfuric acid, 8% zinc sulfate, 21% sodium sulfate, and 0.1% of an ethylene oxide adduct of urea containing 20 ethylene oxide units per'molecule of urea. The

bath was maintained at 60 C. and the extrusion rate.

was about 22 meters per minute. The filaments were subsequently passed through ahot water bath at .9.5?'C.;

and stretched about 82%. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 75% skin and the balance core with a sharp line of dcmarkation between the skin and the core. Other physical properties are set forth in the table which follows the examples.

Example 6 To a viscose as described above, there was added 1% of an ethylene oxide adduct of urea containing 40 ethylene oxide units per molecule of urea. The viscose had a salt test of 10.7 and was spun into a 210 denier, 120 filament yarn by extrusion into a spinning bath containing 7.7% sulfuric acid, 8.6% zinc sulfate, 21% sodium sulfate, and 0.1% of an ethylene oxide adduct of urea containing 20 ethylene oxide units per molecule of urea. The bath was maintained at 60 C. and the extrusion rate was about 44 meters per minute. The filaments were subsequently passed through a hot water bath at 95 C. and stretched about 74%. The yarn was collected in a spinning box, washed free of acids and salts and dried.

The individual filaments were readily distinguishable from control filaments in that they have a smooth, noncrenulated surface and consist entirely of skin while the control filaments have a very irregular and serrated surface and consist of about 75% skin and the balance core with a sharp line of demarkation between the skin and,

Example 7 As a control for the foregoing examples, a viscose solution, prepared as described above, having a salt test of was spun into a 210 denier, 120 filament yarn by extrusion into a bath containing 7.620 sulfuric acid, 8% zinc sulfate and 18% sodium sulfate. The bath was maintained at a temperature of about 60 C. The extrusion rate was about 22 meters per minute. The water bath was maintained at a temperature of about 95 C. and the filaments were stretched 82% while passing through the hot water. The yarn was collected in a spinning box, washed free of acid and salts and dried.

The individual filaments have a very irregular and serrated surface and consist of about 75% skin and the balance core with a sharp line of demarkation between the skin and the core. Other characteristics are set forth in the table which follows.

It will be noted that the tenacity of the filaments of Example 6 is low. This is occasioned by an extrusion rate double of that employed in the other examples. The tenacity may be increased somewhat by employing lower extrusion rates or by reducing to about 0.5% the amount of ethylene oxide adduct of urea added to the viscose.

Although the tenacity and elongation are the only properties set forth, they have been chosen because of the 8 case and simplicity with which such properties may be determined. In some instances, products made in accordance with this invention do not exhibit large or great improvements in tenacity and elongation (Example 4), however, the products consist of a smooth-surfaced, all skin structure and possess improved abrasion resistance, flex-life and other properties as disclosed hereinbefore.

One of the properties of viscose rayon which has limited its uses is its relatively high cross-sectional swelling when wet with water, this swelling amounting to from about 65% to about for rayon produced by conventional methods. Rayon filaments produced in accordance with the method of this invention have an appreciably lower cross-sectional swelling characteristic, the swelling amounting to from about 45% to about 60%.

The modifier of this invention may be added to any desired viscose such as those normally used in industry, the specific viscose composition set forth above, being merely for illustrative purposes. The alkylene om'de adduct of urea or biuret may be added at any desired stage in the production of the viscose and may be present in the cellulosic raw material although it may be necessary to adjust the amount present to produce a viscose having the proper proportions of the adduct at the time of spinnlng.

The term skin is employed to designate that portion of regenerated cellulose filaments which is permanently stained or dyed by the following procedure: A microtome section of one or more of the filaments mounted in a wax block is taken and mounted on a slide with Meyers albumin fixative. After dewaxing in xylene, the section is placed in successive baths of 60% and 30% alcohol for a few moments each, and it is then stained in 2% aqueous solution of Victoria Blue BS conc. (General Dyestuffs Corp.) for 1 to 2 hours. At this point, the entire section is blue. By rinsing the section first in distilled water and then in one or more baths composed of 10% water and dioxane for a period varying from 5 to 30 minutes depending on the particular filament, the dye is entirely removed from the core, leaving it restricted to the skin areas.

This application is a division of my copending application Serial No. 466,679, filed November 3, 1954.

While preferred embodiments of the invention have been disclosed, the descripiton is intended to be illustrative and it is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined by the appended claims.

I claim:

1. A viscose spinning solution containing from about 0.25% to about 4%, based on the weight of the cellulose in the viscose, of a water-soluble reaction product of an alkylene oxide and a substance selected from the group consisting of urea and biuret.

2. A viscose spinning solution as defined in claim 1 wherein the alkylene oxide is ethylene oxide.

3. A viscose spinning solution containing from about 0.5% to about 2.5%, based on the weight of the cellulose in the viscose, of a water-soluble reaction product of ethylene oxide and urea, the reaction product containing from about 4 to about 50 ethylene oxide units per molecule of urea.

4. A viscose spinning solution containing from about 0.5% to about 2.5%, based on the weight of the cellulose in the viscose, of a water-soluble reaction product of ethylene oxide and biuret, the reaction product containing from about 4 to about 5.0 ethylene oxide units per molecule of biuret.

5. A viscose spinning solution containing a small amountof a water-soluble reaction product of an alkylene oxide and a substance selected from the group consisting of urea and biuret, the reaction product containing up to alkylene oxide units per molecule, said small amount of the reaction product being a quantity sufficient to im- 9 part a smooth, non-crenulated surface and a substantially all skin structure to products formed by spinning the viscase at a sodium chloride salt test of at least 7 into an aqueous bath containing from 15% to 22% sodium sulfate from 4% to 9% zinc sulfate and sulfuric acid in an 5 amount not exceeding 8%, but the quantity being insuflicient to adversely afiect the physical properties of such products.

References Cited in the file of this patent UNITED STATES PATENTS Polack July 26, 1938 Cox Dec. 26, 1950 Charles et a1. Dec. 29, 1953 FOREIGN PATENTS Great Britain July 28, 1930 

1. A VISCOSE SPINNING SOLUTION CONTAINING FROM ABOUT 0.25% TO ABOUT 4%, BASED ON THE WEIGHT OF THE CELLULOSE IN THE VISCOSE, OF A WATER SOLUBLE REACTION PRODUCT OF AN ALKYLENE OXIDE AND A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF UREA AND BIURET. 